The dependence of optical band gap Eg and room temperature dark dc conductivity σDRT of rf‐sputtered a‐SiC: H films on substrate temperature Ts and hydrogen flow rate is investigated. For a given hydrogen flow rate, the optical band gap Eg is found to increase as Ts increase up to a critical value, and then decrease upon further increase of Ts. σDRT is found to decrease by about three orders of magnitude as Ts increases, reaching a minimum at 160 and 120 °C for flow rates of 9 and 20 scc, respectively. The conductivity activation energy Ea reaches a maximum, respectively, at the above substrate temperatures. Changes in the hydrogen flow rate from 9 to 20 scc result in an overall increase of the optical band gap by about 0.5 eV, while σDRT decreases by two orders of magnitude. For both hydrogen flow rates, 9 and 20 scc, the Meyer‐Neldel rule is found to hold.
In the present work, the effect of rapid thermal annealing (RTA) on the electrical and structural properties of poly-Si thin films, grown by the crystallization of a-Si films deposited by rapid thermal low-pressure chemical vapor deposition, has been studied. Structural and electrical results were obtained using atomic force microscopy, transmission electron microscopy, electron spin resonance, electrical resistivity, and Hall mobility techniques. The effects of the grain size, grain boundaries, and surface roughness on the electrical characteristics of poly-Si films have been investigated. Amorphous Si (a-Si) films crystallized by RTA at 850 °C for 45 s result in the formation of poly-Si with small grains, an electron spin density Ns=5.2×1016 cm−3, and a Hall mobility μH=30 cm2 V−1 s−1. A two-stage annealing, involving low-temperature annealing at 600 °C for 6 h, followed by RTA at 850 °C in five steps of 30 s each, results in the formation of poly-Si films with large grains free of in-grain defects, low surface roughness, and higher Hall mobility μH=43 cm2 V−1 s−1, characteristics rendering such poly-Si films suitable for the fabrication of good performance thin film transistors.
The fabrication and characteristics of Al/a-Sijcsi(p)/GSi(n+)/Al and Ai/aSiC/c-Si(p)/c-Si(n')/Al switches are presented. Both switches use a non-hydrogenated amorphous thin film. The devices can be optically controlled, and exhibit forward breakover voltages (VeF) of 120-160 V. Their behaviour resembles that of a thyristor. A simple model for the device operation is also presented and discussed for the first time.
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